[RE-wrenches] Temperature coefficient versus Power

[Rebekah Hren]

Hi Jason,
That's an interesting question, as typically it is stated that temperature
coefficients are linear, however the "linearity" is with respect to the
temperature variable, not power (irradiance) I have always assumed that
tkPmp is fairly linear with respect to power, but now that you mention it I
don't have much basis for that assumption!

However, this article
<https://www.sciencedirect.com/science/article/pii/S0038092X21004837>seems
 helpful:
https://www.sciencedirect.com/science/article/pii/S0038092X21004837
Scroll all the way down to section 4.3, and it appears that there are only
very minor variations in tkPMP with low to high irradiance (power).

As that chart shows, tkVoc varies more significantly with irradiance, but I
do think the industry realizes that and factors it in with the allowance in
NEC 690.7 to calculate maximum voltage based on SAND 2004-3535,
Photovoltaic Array Performance Model, which takes into account the
effect that low irradiance has on voltage - you can see the lower tkVOC at
lower irradiances.
Cheers,
Rebekah



Licensed Electrical Contractor
NABCEP Certified Solar PV Installation Professional™ 091209-85
Tel: 336.266.8800



On Tue, Jan 30, 2024 at 9:04 AM Jason Szumlanski via RE-wrenches <
re-wrenches at lists.re-wrenches.org> wrote:

> I'm having a hard time finding concrete information on the relationship of
> temperature coefficient and power output. Solar panel temperature
> coefficients are determined at Pmax.
>
> My question is, at lower irradiance levels, say where power output would
> be 50% of Pmax at 25C, would the temperature coefficient be greater, less,
> or the same?
>
> Jason Szumlanski
> Florida Solar Design Group
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